Method for preparing fatty esters of non-reducing oligosaccharides in the presence of an amide



Unite Nathaniel Beverly Tucker, Cincinnati, The Procter & GambleCompany, Cli corporation of Ohio N0 Drawing. Application December 15,1955 Serial No. 553,198

Claims. or. 260-234) This invention relates to a process for preparingfatty esters of oligosaccharides, and more especially to the preparationof fatty esters of non-reducing oligosaccharides, such as sucrose.

Many methods of preparing fatty esters of polyhydric alcohols, sucroseand other non-reducing oligosaccharides are known and have beenheretofore employed. Among these are: the direct esterification of thealcohol or oligosaccharide and fatty acids; the reaction of the alcoholor oligosaccharide with fatty acid anhydrides; the reaction of thealcohol or oligosaccharide with fatty acid halides; and thereesterification. of fatty acid esters with polyhydroxy alcohols.Various disadvantages are identitied with these processes such as, forexample, poor yields, excessive time to carry the reaction to thedesired cornpleteness, and excessive temperatures necessary to pro-Other objects and disadvantages will be apparent from A the followingdetailed description.

I have found that these objects can be accomplished by subjecting tointeresterification a mixture of a nonreducing oligosaccharide and afatty acid ester of an aliphatic primary monohydroxy alcohol or a fattyacid ester of a polyhydroxy alcohol in the presence of certain amides inwhich the reactants exhibit some mutual solubility.

Generally speaking, the invention contemplates reacting the non-reducingoligosaccharides with the fatty acid ester in the presence of analkaline catalyst, which shows activity in interesterificationreactions, at a temperature in the range from about to about 150 C., andin the presence of an amide compound of the general formula CHQCHQ NRcrncm Where X is selected from the group consisting of oxygen and CH andR is an acyl radical selected from the group consisting of formyl,acetyl and propionyl radicals. Fol lowing completion ofinteresterification to the desired degree, the catalyst is inactivatedby the addition of water and/or acids such as acetic, phosphoric,citric, hydrochloric, and the like, and the desired reaction productsare freed of solvent and purified by any suitable means.

The term oligosaccharides is used herein to differentiate the di, tri,and tetra-saccharides as a group, from the polysaccharides which arecomposed of a much greater number of single units. Of theoligosaccharides, I have found that only those of the non-reducing type,i. 6., those having no potentially free aldehyde or ketonic group, are

States Patent 0 ice suitable for purposes of this invention. Theseinclude the disaccharides; sucrose, trehalose and glucoxylose; thetrisaccharides; raffmose, melezitose and gentianose; and thetetra-saccharide, stachyose. Thus, the oligosaccharides of concern hereare non-reducing polyhydroxy compounds having from 7 to 16 hydroxylgroups per molecule.

The fatty esters which can be employed in the reaction herein concernedare the fatty acid esters of primary aliphatic monohydroxy alcoholshaving from 1 to 16 carbon atoms, for example, methanol, ethanol,hexanol, decanol, dodecanol, and hexadecanol, specific examples beingmethylpalmitate, dodecylpalmitate and hexadecylpalmitate. In addition,fatty acid esters of completely or incompletely esterified polyhydricalcohols having from 2 to 6 hydroxyl groups, such as glycol, ethyleneglycol, glycerol, erythritol, pentaerythritol, mannitol, and sorbitolcan be employed. Glycol dipalmitate, glycerol mono-, di-, andtripalmitate, mannitol partial palmitates, erythritol tetrapalmitate,pentaerythritol tetrapalmitate and sorbitol hexapalmitate are examplesof operative fatty esters. In addition, fatty esters of glycosides, suchas methyl glucoside tetrapalmitate, can be employed. The use of fattyacid esters of the aforementioned oligosaccharides having from 7 to 16hydroxyl groups in the molecule is also contemplated. Thus, just asmono-, and diesters of glycerol can be prepared from the triglyceride,so incompletely esterified sucrose esters can be prepared in accordancewith the present invention by reaction of sucrose with completelyesterified sucrose. Thus, the reaction of sucrose octapalmitate withsucrose can be carried out advantageously with the aid of the presentinvention.

The aforementioned polyhydric alcohols and non-reducing oligosaccharidesconsidered as a group will for purposes herein be referred to asaliphatic alcoholic polyhydroxy substances.

The length of the fatty acid chain of the esters above designated is notcritical and is dictated primarily by the type of fatty acid materialsource available. For my purposes, however I have found that fatty acidscontaining from about 8 to 22 carbon atoms are most useful. Thus, themixtures of fatty acids obtained from animal, vegetable, and marineoils, and fats, such as coconut oil, cottonseed oil, soybean oil,tallow, lard, herring oil, sardine oil, and the like, representexcellent and valuable sources of fatty acid radicals. in the event itis desired to produce oligosaccharide esters of single fatty acids bythis invention, then the fatty acid esters of relatively volatilealcohols (e. g. methanol and ethanol), having from about 12 to about 22carbon atoms can be reacted with the non-reducing oligosaccharide withthe aid of the particular amide reaction medium herein covered.

Of the fatty esters which may be used in the practice of my invention Iprefer to use the esters of those alcohols having not more than threecarbon atoms.

The crux of my invention lies in the selection of the solvent whichcomprises the reaction medium. The choice of solvent is essential to therealization of rapid and efficient interesterification of thenon-reducing oligosaccharide and the fatty ester under the conditionshereinbefore set forth. i have found that in general thenitrogensubstituted amide compounds as hereinbefore defined areeminently suitable as solvents in my process. These compounds promote arapid rate of reaction with minimum catalyst requirements and undergo aminimum of decomposition during the interesterification reaction.

With these amide solvents I have found in general that the rate ofinteresterification decreases with increase in molecular Weight of theamide; that solvent volume requirements in the reaction decrease withincreasing solubility of the non-reducing oligosaccharide in thesolvent; and that the solubility of the non-reducing oligosacamount ofsolvent required for any given interesterification will varyldependingupon the particular solventwhich is to be used, the actual amount ofsolvent is not critical. Amounts of solvent from /3 to 50 times byweight of the fatty ester employed for reaction with the oligosaccharidefind application in my process. It is to be understood, however that thesolvent usage is normally adjusted depending upon the particularreactants to be interesterified. In any event, sufiicient solvent shouldbe used so that the advantages associated with solvent usage may berealized.

The proportion of reactants is not critical and is dictated primarily bythe ultimate product which is desired. For example, in the reaction ofsucrose with fatty ester, proportions can be chosen so that from one toall of the hydrogen atoms of the hydroxyl groups of sucrose may bereplaced by fatty acyl radicals. Or, where sucrose and a triglycerideare being reacted, proportions can be chosen soth'at the final productmay predominate in either glycerides or sucrose esters. As a practicalmatter, however, molar ratios of non-reducing oligosaccharide to fatty iester in the range from about 30:1 to about 1:20 are most satisfactory,the proportions being variable Within the range depending on thecompleteness of replacement desired and on the number of fatty acidradicals in each mole of ester substance. Thus, for example, if 0.1 moleof methylpalmitate is reacted with 1 mole of sucrose under thehereinbefore defined conditions and at reduced pressure essentially allof the sucrose ester formed will be monoester. If the molar ratio ischanged to 1:1, one obtains a high yield of monoester of sucrose, butmore diester will be present. A product averaging approximately 2palmitic acid groups per mole of sucrose may be obtained with a molarratio of methylpalmitate to sucrose of 2:1. When molar ratios of 4:1,8:1, or 10:1 are used the average number of palmitic acid radicals permole of sucrose obtained may be 3.5, 6, or 7.5.

Although my process is illustrated herein principally with the use ofsodium methoxide as the catalyst, effective practice of the process isnot dependent u on the use of any particular catalyst. Rather, anyalkaline molecular rearrangement or interesterification catalyst whichwill pro-mote the interchange of radicals among the reactants of myprocess is suitable. Examples of usable catalysts are: sodium methoxide,anhydrous potassium hydroxide, sodium hydroxide, metallic sodium, sodiumpotassium alloy, and quaternary ammonium bases such as trimethyl benzylammonium hydroxide. A discussion of other catalysts which are active ininteresterification reactions may be found in U. S. Letters Patent2,442,532, to E. W. Eckey, column 24, line 18 et seq.

The sodium methoxide catalyst may be advantageously used in my processin amounts from about 0.05% to about 2.0% by weight of the fatty esterwhich is to be reacted, equimolar amounts of other catalysts beingusable. The choice of catalyst and the amount which is to be used are ofcourse dependent upon the particular constituents which are to bereacted.

, In the practice of the invention, it was observed that the reactionrate for a given solvent usage and a given catalyst increased withincrease in temperature. With optimum amounts of formyl piperidine, forexample, and with sodium methoxide as the catalyst, at temperatures of100 C. I found that equilibrium was reached after about 20 minutesreaction time and that somewhat longer reaction times were required atlower temperatures. How ever, substantial ester formation was observedat reaction temperatures as low as -40 C. Where low temperatures such as20 C. are employed for special purposes,

longer reaction times are required to achieve desired ester formation.Temperatures above 100 C., such as 150 C. may, of course, be employed,but in view of the high rate of reaction observed in use of the solventsof the present invention, such temperatures may only infrequently benecessary to accomplish the desired ester formation. Generally speaking,with any of the aforementioned reactants, catalysts, or solvents andwithin the ranges of proportions set forth, the process of my inventionis preferably carried out at a temperature in the range from about toabout 150 C.

Although my process is normally carried out at atmospheric pressure, itcan if desired be carried out under reduced pressure, an operation whichat times'is decidedly advantageous. For example, when a fatty acid esterof methanol is reacted with sucrose, operation under reduced pressure,such as about 80 mm. of mercury, enables the methanol formed as a resultof the interesterification to be removed from the reaction zonesubstantially as rapidly as it is liberated, thus promoting asubstantially complete conversion of the methyl ester to sucrose fattyester.

Since the reaction of the present invention is an interesterification inwhich sucrose, for example, is reacted with a fatty ester, the resultingproduct of the reaction will constitute an equilibrium mixture ofsucrose, esters thereof, displaced alcoholic substance from the esteroriginally employed, and ester of such alcoholic substance. Thus, iftriglycerides are reacted with the sucrose, then the product of thereaction will contain monoand diglycerides as well as sucrose esters. Ifit is desired to obtain sucrose esters which are not so contaminatedwithoriginal esters and derivatives thereof, then it is preferable toreact volatile alcohol esters such as methyl or ethyl esters with thesucrose and, as suggested above, to conduct the reaction under vacuum sothat displaced alcohol is distilled olf. High yields of sucrose estersare obtainable in this way and, of course, unreacted volatile esters canbe separated subsequently by distillation to yield sucrose esters ofhigh purity.

One way of determining whether or not ester has been formed when workingwith the oligosaccharides is by observing the optical activity of therecovered reaction product. As is well known, sucrose and otheroligosaccharides have optical activity which may be readily determinedin the usual way by polarimetric measurement. in the present case,specific rotation figures have been determined by means of a RudolphModel 70 polarimeter, using a filtered light source of 546 millimicronswave length. The rotation is measured at room temperature (2527 C.) inpyridine solution at a concentration of about 2% using a sample lengthof 10 cm. Under such conditions of observation, sucrose shows a specificrotation of The esters formed from sucrose also possess optical activityand since the method of recovery, as shown in the examples to follow,eliminates contamination of the product with water soluble substancessuch as sucrose, then any optical activity of the product recovered isindicative of a content of sucrose ester. For example, themonopalrnitate ester of sucrose has a combined sucrose content of 59%and a specific rotation of 59 to 60 under the above conditions.

Although optical activity can not be accepted as an absolute measure ofthe percent oligosaccharide content of the ester unless the exact natureof the ester is known, there is a close correlation between the percentcombined sucrose content and the observed specific rotation. Thus, forexample, the specific rotation of the octa ester of sucrose will besubstantially less than the mono-ester of sucrose because of its lowercontent of combined sucrose. Moreover, the specific rotation of theproduct will depend on the nature and concentration of theoligosaccharide ester, whatever it is, in the product being measured.Thus, figures for specific rotation, sometimes designated as [0:1 areindicative of ester formation in the interesterification reaction, thedegree of esterification being indicated by other characteraesneocistics such as hydroxyl value, saponification value, and total fattyacid content as determined by procedures well known in the art.

The following examples will illustrate the manner in which the inventionmay be practiced. It will be understood, however, that the examples arenot to be construed as limiting the scope of conditions claimedhereinafter.

Examples 1, 2, 3, 4 and 5 A number of amide compounds coming within thescope of the definition hereinbefore given were employed in theformation of sucrose esters. In each case grams of sucrose, 18 grams ofa mixture of 80% soy bean oil and 20% cottonseed oil hydrogenated to aniodine value of about 76, 100 milliliters of the amide reaction mediumwere mixed and heated to 100;*:3 C. After the above temperature wasreached 0.18 gm. of sodium methoxide catalyst was added to the heatedmixture and the interesterification reaction was allowed to proceed. Atvarious time intervals after the addition of the catalyst, 20 milliliteraliquots were removed from the reacting mixture and the catalyst inthese aliquots was inactivated by the addition thereto l milliliter of a50% aqueous solution of acetic acid. Following inactivation of thecatalyst the aliquot was taken up in 50 ml. of a 4:1 mixture of ethylacetate and n-butanol and water washed. The water washed fatty productswere recovered by evaporating the ethyl acetate-n-butanol solvent on asteam bath under a stream of nitrogen. The recovered reaction productwas measured for optical activity in accordance with the proceduredescribed hereinbefore. In the following table the results are givenshowing substantial production of sucrose ester in all cases.

Specific Rotation After Minutes of React. Time Amide Solvent 1 Takenafter 210 minutes reaction time. 1 Taken after 90 minutes reaction time.

It is to be understood that in the foregoing examples the sucrose may bereplaced by any of the non-reducing oligosaccharides with comparableresults.

Having thus described my invention, I claim:

1. A process for preparing fatty esters of non-reducing oligosaccharideswhich comprises reacting a non-reducing oligos'accharide with a fattyacid ester selected from the group consisting of fatty acid esters ofaliphatic primary monohydroxy alcohols having from 1 to 16 carbon atomsand fatty esters of aliphatic alcoholic polyhydroxy substances, thefatty acid chain of the said fatty esters containing from about 8 toabout 22 carbon atoms in the presence of an interesterificationcatalyst, at a temperature in the range from about 20 to about 150 C.and in the presence of an amide of the general formula:

where X is selected from the group consisting of oxygen and CH, and R isan acyl radical selected from the group consisting of formyl, acetyl andpropionyl radicals, the said non-reducing oligosaccharides being in amolar ratio to the said fatty acid ester of from about :1 to about 1:20and the amide being present in an amount from /3 to 50 times by weightof the said fatty acid ester.

2. The process of claim 1. wherein the non-reducing oligosaccharide issucrose.

3. The process of claim 1 wherein the amide is formyl piperidine.

4. The process of claim 1 wherein the amide is formyl morpholine.

5. The process of claim 1 wherein the amide is acetyl morpholine.

6. A process for preparing fatty esters of sucrose which comprisesreacting sucrose with a fatty acid ester selected from the groupconsisting of fatty acid esters of aliphatic primary monohydroxyalcohols and the fatty acid esters of polyhydroxy alcohols, the fattyacid chain of the said fatty esters containing from about 8 to about 22carbon atoms, all of said alcohols having not more than three carbonatoms, in the presence of an interesterification catalyst, at atemperature in the range from about to about 150 C. and in the presenceof an amide of the general formula where X is selected from the groupconsisting of oxygen and CH and R is an acyl radical selected from thegroup consisting of formyl, acetyl and propionyl radicals.

7. A process for preparing fatty esters of sucrose which comprisesreacting sucrose with a fatty acid ester 7 of glycerol containing fromabout 8 to about 22 carbon atoms in the fatty acid chain, in thepresence of from about 0.05 to about 2% of an interesterificationcatalyst, by weight of the glycerol ester, at a temperature in the rangefrom about 80 to 150 C. in a reaction medium comprising essentiallyformyl morpholine.

8. The process of claim 7 wherein the fatty acid ester is atriglyceride.

9. A process for preparing fatty esters of sucrose which comprisesreacting sucrose with a fatty acid ester of methanol containing fromabout 8 to about 22 carbon atoms in the fatty acid chain, in a reactionmedium comprising essentially formyl morpholine in the presence of fromabout 0.05 to about 2% of an interesterification catalyst, by weight ofthe methyl ester, at a temperature in the range from about 80 to about150 C. and at such a sufficiently low pressure that the methanolliberated during the reaction is continuously distilled from thereaction mix whereby the reaction proceeds to substantial completeness.

10. The process of preparing fatty esters of sucrose which comprisesreacting sucrose and a fatty triglyceride containing from about 8 toabout 22 carbon atoms in the fatty acid chain, in the presence of aninteresterification catalyst at a temperature of about C. in a reactionmedium comprising essentially formyl morpholine, inactivating thecatalyst by acidulation, distilling substantially all of the formylmorpholine. from the reaction mixture and water-washing the residuewhereby undistilled solvent and unreacted sucrose are removed therefrom.

Journal of The American Oil Chemists Society, July 1948, pp. 258-260.

1. A PROCESS FOR PREPARING FATTY ESTERS OF NON-REDUCING OLIGOSACCHARIDESWHICH COMPRISES REACTING NON-RE DUCING OLIGOSACCHARIDE WITH A FATTY ACIDESTER SELECTED FROM THE GROUP CONSISTING OF FATTY ACID ESTERS OFALIPHATIC PRIMARY MONOHYDROXY ALCOHOLS HAVING FROM 1 TO 16 CARBON ATOMSAND FATTY ESTERS ALIPHATIC ALCOHOLIC POLYHYDROXY SUBSTANCES, THE FATTYACID CHAIN OF THE SAID FATTY ESTERS CONTAINING FROM ABOUT 8 TO ABOUT 22CARBON ATOMS IN THE PRESENCE OF AN INTERESTERIFICATION CATALYST, AT ATEMPERATURE IN THE RANGE FROM ABOUT 20* TO ABOUT 150*C. AND IN THEPRESENCE OF AN AMIDE OF THE GENERAL FORMULA: